1. Field of the Invention
The present invention generally relates to an improved temperature-controlled fan fluid coupling which controls the rotation of a fan for cooling an automotive engine in such a way that the amount of cooling air supplied to the engine always corresponds to the temperature around the engine while the automobile is running.
2. Description of the Prior Art
Main portions of a conventional fan fluid coupling of this kind are shown in FIG. 12. This fluid coupling comprises a casing 22, a cover 23 forming an enclosed housing, a partition plate 25 provided with an outflow-adjusting hole 25', a torque transmission chamber 24, an oil reservoir chamber 26, a single valve member 28, and a drive disk 27 having a communication hole 27'. The outflow-adjusting hole 25' is located on the side of the torque transmission chamber 24. The valve member 28 is located on the side of the oil reservoir chamber 26 and mounted at its one end to the partition plate 25. The valve member 28 opens or closes the hole 25' to increase or decrease the effective area in contact with oil in the torque transmission gap. In this way, the transmitted torque is controlled.
In the above-described prior art technique, the single outflow-adjusting hole 25' is opened or closed by the single valve member 28. Thus, the coupling can assume only two states, i.e., the coupling is disengaged or engaged. The output rotational frequency characteristic is shown in FIG. 13. As can be seen from this graph, the transmitted torque changes suddenly at a predetermined temperature. Therefore, the amount of cooling air becomes excessive or insufficient at temperatures close to the predetermined temperatures. Also, fan noise is induced by these functions. Furthermore, the bearing and the fan members get fatigued quickly and may become damaged or deformed.